The expressions "live tapping" and "hot tapping" refer to the cutting or drilling of a hole through the wall of a vessel or a pipe while the same contains a fluid under pressure. This procedure is typically performed in those circumstances where it is desired to make a connection to the pipe without taking the pipe out of operation and without removing pressurized fluid from it. This kind of tapping, for example, is often utilized for connecting into a pipeline carrying a domestic water supply, since it would be a substantial inconvenience to have to shut down the entire line.
Live tapping is typically carried out by first welding a stub pipe or a split T to the pipe, and then mounting a tapping valve on the stub or on the branch of the T. A tapping apparatus can be mounted on the valve with its cutter running through the open valve to cut the opening in the pipe. After the opening has been cut, the cutter is retracted and the valve closed, whereupon the tapping apparatus can be removed without any substantial leakage of fluid into or out of the pipe. It is also known to utilize a "saddle" which surrounds the pipe and provides a recessed area containing a flat seal. The saddle is adapted to be tightened around the pipe and has a threaded collar or the like projecting away from the pipe at the location of the seal, as well as an opening such that a cutting device or bit can pass through the opening to cut into the pipe.
Currently, the apparatus which controls the cutting device and which is threadably attached to the saddle or equivalent, must be sized in such a way that it is adapted to the particular cutting device. Generally it is found that an apparatus suitable for a short cutting device such as a circle cutter is inappropriate for use with an elongated drill bit. The problem is largely due to the fact that a shaft that is small enough to pass through small diameter valves and place a cutting device in position against the pipe would not be sufficiently strong to operate it. Therefore, elongated drills that will contact the pipe through the valve are used.